1. Field of the Invention
The present invention relates to an electric motor, a rotary actuator that is provided with this electric motor, and a rotary apparatus that uses this rotary actuator.
2. Description of Related Art
The conventional technology of a rotary actuator and an electric motor provided for a rotary actuator is illustrated in Japanese Unexamined Patent Application, First Publication No. 2004-52928.
This rotary actuator is constructed by placing a synchronous electric motor and an internally-meshing planetary reduction gear which is connected to a rotor shaft (i.e., a first shaft) of this synchronous electric motor inside a single housing. This internally-meshing planetary reduction gear is provided with an external gear, an internal gear which internally meshes with this external gear, and a second shaft. The external gear is mounted on the internally-meshing planetary reduction gear in a state in which it is able to perform an eccentric rotation via an eccentric shaft portion that is provided at a position partway along the rotor shaft. The second shaft is linked to the internally-meshing planetary reduction gear via a transmission unit that only transmits the rotation components of the external gear.
In this case, a portion of the second shaft is formed as a cylinder, and the second shaft has a dual bearing structure in which the second shaft itself is rotatably supported in the housing via metal bearings, while the rotor shaft is rotatably supported via internal bearings inside the second shaft.
Three shaft portions, namely, the rotor shaft, the eccentric shaft portion, and the second shaft are provided in this type of conventional rotary actuator. Because of this, a total of four bearings are required to support these shaft portions, namely, one bearing at each end of the rotor shaft, one bearing for the eccentric shaft portion, and one bearing for the second shaft. In addition, two bearings are also required on the output side, so that a total of six bearings are required. In this manner, in a conventional rotary actuator, the problem arises that there are a large number of components.
Furthermore, as is described above, the second shaft has a dual bearing structure. Because the rotor shaft of the electric motor is supported inside the second shaft, the coaxial accuracy of this rotor shaft often deteriorates resulting in there being a tendency for vibration to occur. Because of this, in a conventional rotary actuator, it is necessary to ensure there is a large air gap between the rotor and the stator of the electric motor. Consequently, there is a tendency for the performance and efficiency of the electric motor to deteriorate.
Moreover, the above described electric motor according to the conventional technology is constructed by assembling various electrical components such as a rotor, a stator, and a board inside a housing. Here, one end portion of the shaft of the rotor is supported via a bearing by a front housing which forms one housing, while another end portion of the shaft of the rotor is supported via a bearing by a rear housing which forms another housing. Moreover, the board is fixed to the rear housing side, and a number of electrical components such as the rotor and stator are stacked in the axial direction of the rotor shaft from above the board.
Accordingly, when this type of electric motor is being assembled, it is necessary to fix the board at a comparatively early stage, and then electrically connect the board to terminals of the various electrical components using solder or the like prior to the board being covered by the other electrical components when they are assembled thereon.
However, when, as in the above described conventional electric motor, the task of assembling a large number of electrical components still remains after the above described electrical connections have been made, these electrical connections are affected by the subsequent assembly task. As a result, there is a possibility that the electrical reliability of the electric motor will deteriorate.
Furthermore, in the above described conventional electric motor, because a structure is employed in which the stator is assembled inside the housing, errors occur when the stator is being assembled in the housing so that it is difficult for the axial accuracy of the rotor and stator to be set to a high level. In this case, it is necessary to ensure there is a large air gap between the rotor and stator. Consequently, there is a tendency for the performance and efficiency of the electric motor to deteriorate.
The present invention was conceived in view of the above described circumstances, and it is a first object thereof to provide a rotary actuator and a rotation apparatus that uses this rotary actuator, in which the number of components is reduced, and in which the coaxial accuracy of the electric motor relative to the rotor shaft is increased, so that the performance and efficiency thereof are improved.
Moreover, it is a second object of the present invention to provide an electric motor and a rotary actuator which is provided with this electric motor, that enable electrical reliability to be improved.
Furthermore, it is a third object of the present invention to provide an electric motor and a rotary actuator which is provided with this electric motor, that enable the axial accuracy of the stator to be increased so that the performance and efficiency of the electric motor are improved.